Mold for castings of iron and nonferrous metals



UNITED STATES PATENT OFFICE MOLIl FOR CASTINGS OF 'IRON AND NONFERROUSMETALS Max Heusser, Winterthur, Switzerland No Drawing. .ApplicationDecember 11, 1931, Serial No. 580,506. In Switzerland December 13, 19306 Claims. (01. 22188) It is known that the size of grain in thestrucmaking molds can now. not only fill out by steps ture of a castingdepends to a large degree on the interval at present existing betweenthe therthe rate of cooling and therefore on the thermal malconductivity of the usual material and the conductivity of the mold.When the heat is led thermal conductivity of iron, but it can alsobeaway slowly from the mold, and the casting is come greater than thethermal conductivity of therefore cooled slowly, the structure of thecastiron.

ing is open grained, whilst when cooling or heat According to theinvention, graphite is preftransmission through the material of the moldis erably used as the material, or as a constituent of more rapid, afine-grained structure is obtained. the mixed materials, for making themolds. The

10 It is not yet known to make any use .of this coefficient of heattransmission of graphite in fact, since the known methods of improvingthe the solid state is 0.105 cal./cm/second/degree C. quality ofcastings by adopting molds made of when unheated, and 0.28 atatemperature of 555 metal, through which the thermal conductivity at C.(according to Landolt-Bornstein, Physikalischcertain parts shall bechanged as compared with chemische Tabellen, 5th edition and supplemene15 that at other parts, have the disadvantage that tary volume, 1927).in consequence of the sudden variation of the If the coefficient of heattransmission of the thermal conductivity of the material used, greatusual foundry sand is taken as 1, the coefficient difierences occur inthe quantities of heat transof heat transmission for cast iron is thenabout mitted from the casting. This leads to an all too 250, and of thenew molding substance using solid 0 rapid chilling and consequently anundesirable graphite, about 180 when unheated and about 470 hardness ofthe material, so that not only is anat a temperature of 555 C. nealingrequired in order to make the structure Whilst the conductivity of thecast iron used for more uniform, but difliculties for machining aremolds is 250 times greater than that of the usual also created. Theknown method of coating the foundry sand, and consequently also, whenboth 2 surface of the mold with graphite cannot reduce substancesareused simultaneously beside each 89 this injurious efiect, since itsolely prevents the other, the transmission of heat at a certain spotmold burning and has .no influence worth'menis 250 times greater thanthat at a neighboring tioning on the thermal conductivity of thematespot, 1. e. it suddenly changes; but on the other rial of the mold.hand the conductivity of the new materialfor 30 The purpose of thisinvention is to control the making molds changes gradually or by stepsuntil rate of cooling of the casting and thereby the it is 470 timesgreater than the conductivity of formation of the structure by gradingthe coeifithe usual foundry sand, the figure depending on cient of heattransmission or the conductivity whether, it is unmixed, in the form ofpowder, in of the material used for the mold, in such a way solid formor at a high temperature; consequently 35 as to improve the quality ofthe casting. The inthe thermal conductivity can be changed as re- 90vention consists in mixing into the substance quired within the limitsmet with in practice. used for the mold, a material the thermal con- Byaltering the proportions of the materials ductivity of which in theunheated state is lower used for making molds, the coefficient of heatthan that of iron but greater than that of sand, transmission can begradually, and not only sud- 40 and which is also highly refractory.Preferably denly, changed, thereby increasing the qualities thematerial, used by iself or as an admixture to of the casting, withoutany drawbacks for the maothers, will have in the unheated state athermal chining or for any other later process having to" conductivitylower than that of iron, but increasbe put up with. ing with increasingtemperatures until it is above I claim:

45 that of iron. A suitable material to use for regu- 1. A mold forcasting metals comprising moldlating the thermal conductivity or heattransmising sand and a material, which in an unheated sion of thesubstance used for the mold is graphite. state, has a coefficient ofthermal conductivity The invention is based on adopting for the moldlower than that of iron and greater than that of a material which, ascompared with materials the molding sand, said material being non-uni-50 hitherto used for this purpose, possesses a very formly distributedthroughout the molding sand variable thermal conductivity. Thecoeflicient of and being present in greater proportion at those heattransmitted M for a certain cast iron is for places where heat is to beremoved more rapidly. example 0.,15 cal/sq. cm./second/degree C., the 2.A mold for casting metals comprising moldcoefficient x2 for a typicalfoundry sand is 0.0006. ing sand and a material which, in an unheated 55The thermal conductivity of the new substance for state, has acoefficient of thermal conductivity lower than that of iron and greaterthan that of the molding sand, andwhich, when heated to castingtemperatures, has a coeflicient of thermal conductivity greater thanthat ofiron, said material being non-uniformly distributed throughoutthe molding sand and being present in greater proportion at those placeswhere heat is to be removed more rapidly.

3. A mold for casting metals comprising molding sand, and graphitenon-uniformly distributed throughout the molding sand and being presentin greater proportion at those places where heat is to be removed morerapidly.

4. A mold for casting metals comprising molding sand and a materialwhich, in an unheated state, has a coefiicient of thermal conductivitylower than that of iron and greater than that of molding sand, saidmaterial being non-uniformly distributed throughout the molding sand,the

molding sand being free from inclusion of said material at places wherethe cast object has the least wall thickness, and the material beingpresent in progressively increasing amounts to places where the castobject has the greatest wall thickness, so that the conductivity and thecooling rate at difi'erent places of the cast object are in accordancewith the heat to be removed at those places for the purpose of improvingthe structure of the casting. 1

5. A molding for east metals comprising molding sand and amaterialwhich, in an unheated state, has a coeflicient of thermalconductivity lower than that of iron and greater than that of moldingsand, and which, when heated to casting temperatures, has a coefficientof thermal conductivity greater than that of iron, said material beingnon-uniformly distributed throughout the molding sand, the molding sandbeing free from inclusion of said material at places where the castobject has the least wall thickness, and the material being present inprogressively increasing amounts to places where the cast object has thegreatest wall thickness, so that the conductivity and the cooling rateat difierent places of the cast object are in accordance with the heatto be removed at those places for the purpose of improving the structureof the casting.

6. A molding for casting metals comprising molding sand, and graphitenon-uniformly distributed throughout the molding sand, the molding sandbeing free from inclusion of the graphite at places where the castobject has the least wall thickness, and the graphite being present inpro- 1 gressively increasing amounts to places where the cast object hasthe greatest wall thickness, so that the conductivity and the coolingrate at different places of the cast object are in accordance with theheat to be removed at those places for the purpose of improving thestructure of the casting.

MAX HEUSSER.

